The American actress has been dating the Muse rocker for around nine months, with the two becoming inseparable as soon as they got together. Kate is pregnant with their first child together and the couple are now believed to have secretly got engaged.
They reportedly held a party for their friends and family in a London hotel on Monday where they broke the exciting news to their loved ones.
"It was an intimate party,” a source told British newspaper The Sun. “They kept their engagement secret as they wanted to celebrate with their nearest and dearest before it became public knowledge."
Further details about the date and venue for the forthcoming nuptials are not yet known.
Kate’s mother Goldie Hawn attended the party on Monday after flying into the UK last weekend to attend an awards ceremony. She has revealed she is thrilled Kate is pregnant and has found love with Matt, 32. "I'm excited - happy for them both," she said last week.
Kate already has seven-year-old son Ryder with her ex-husband Chris Robinson. The 31-year-old actress is reportedly excited to be giving her son a sibling, as it’s what she has always wanted.